The invention relates to turbogenerators, and more particularly to control methods and systems for turbogenerators.
A turbogenerator is typically operated at a steady state condition defined by certain temperature, speed, fuel flow, and other parameters selected to meet a specified power output. When the required power output drops suddenly, such as may occur when the turbogenerator is operated to meet a certain power demand and the power demand experiences a transient drop, one or more of the parameters must be adjusted accordingly to produce only the required power and, optionally, dispose of any excess power being generated. Typically, the fuel flow provided to the turbogenerator must decrease to a reduced level to sustain a lower turbogenerator speed as dictated by the new, reduced power demand. Reducing the fuel flow will also typically reduce the turbine exhaust temperature (herein after: TET). Both the fuel flow and the TET, however, are subject to the certain operating constraints. TET, for instance, cannot exceed certain values for certain periods of time without causing significant damage to the turbogenerator components. Fuel flow cannot be reduced below a certain predetermined level without causing flame-out in the turbogenerator combustor.
What is therefore needed is a method and system for transient turbogenerator control that prevents combustor flame-out.
In one aspect, the invention provides a method of controlling a turbogenerator comprising operating the turbogenerator at a selected speed to provide a selected amount of power, providing fuel to the turbogenerator to maintain a turbine exhaust temperature at a first selected value, reducing the turbogenerator speed to provide a reduced amount of power, and providing fuel to the turbogenerator to maintain the turbine exhaust temperature at a second selected value higher than the first selected value for a selected period of time.
In another aspect, the amount of fuel provided to the turbogenerator is gradually increased over the selected period of time to maintain the turbine exhaust temperature at the second selected value. In a further aspect, the turbogenerator speed is reduced to provide a reduced amount of power in response to a reduction in a power demand. A specified period of time may be allowed to lapse after the reduction in power demand prior to reducing the turbogenerator speed.